Phosphoric acid esters of polyoxyalkylenated gelatin as sensitizers

ABSTRACT

SENSITIZERS FOR LIGHT-SENSITIVE PHOTOGRAPHIC SILVER HALIDE EMULSIONS COMPRISING WATER-SOLUBLE PHOSPHORIC ACID ESTERS OF POLYOXYALKYLENATED GELATIN.

United States Patent O 3,558,321 PHOSPHORIC ACID ESTERS OF POLYOXYAL. KYLENATED GELATIN AS SENSITIZERS E Scudder Mackey and Fritz Dersch, Binghamton, N.Y., and Fred S. Eiseman, Maplewood, N.J., assignors to GAF Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Jan. 6, 1967, Ser. No. 607,669

Int. Cl. G03c 1/28 U.S. Cl. 96-107 6 Claims ABSTRACT OF THE DISCLOSURE Sensitizersfor light-sensitive photographic silver halide emulsions comprising water-soluble phosphoric acid esters of polyoxyalkylenated gelatin.

The present invention relates in general to the provision of novel additives for improving the sensitivity, anti-static properties, contrast, covering power, etc. of photographic silver halide emulsions and in particular to the employment of certain gelatin derivatives for such purposes. t

As is well known, the sensitivity of light-sensitive silver halide emulsions can be increased in a number of ways as for example by the incorporation therein of one or more chemical or optical sensitizing agents which function to augment and/or extend the emulsion sensitivity to light of longer wave lengths.

In general, it is postulated that chemical sensitization results from the formation of small amounts of silver sulfide and/or silver on the surface of the silver halide crystal. As examples of compounds found to function as chemical sensitizing agents there may be mentioned sodium sulfite, sodium thiosulfate and the like.

Heretofore, a wide variety of compounds has been suggested for purposes of increasing the spectral sensitivity of photographic silver halide emulsions. Particularly beneficial results are purportedly obtained with such compounds as the polyoxyalkylene ethers and numerous derivatives thereof such as the products obtained by reacting alkylene oxide with reactive hydrogen-containing organic compounds, e.g., acids, alcohols, amines, etc. The use of the foregoing and related compounds for such purposes is well established in the prior art being extensively described in the patent and trade literature. Other compounds proposed for use in a similar relationship include the quaternary ammonium, phosphonium and ternary sulfonium salts as well as combinations or mixtures of one or more of the foregoing compounds with alkylene oxide polymers.

Other problems frequently encountered in the emulsion-making as well as the emulsion-processing industries relate to the production of relatively high speed emulsions which enable the attainment of image reproductions characterized by satisfactory contrast as well as covering power of the developed silver. As is well known, the term covering power is a measure of the silver concentration in the developed image and is derived arithmetically by dividing the optical density at maximum density by the grams of silver per square decimeter in the developed image layer.

As examples of materials heretofore promulgated for use as emulsion addenda to thereby obtain the requisite contrast, silver covering power, etc., there may be mentioned in particular the poly-N-vinyl lactams, the watersoluble polyglucose dextrans, water-soluble B-hydroxyalkyl ethers of polyvinyl alcohol water-soluble hydrolyzed glycogen, water-soluble mannan polysaccharide, the water-soluble polyglucose laminarins, hydroxy-ethyl cellulose, carboxy-methylated proteins and the like.

Patented Jan. 26, 1971 P ce While the foregoing and related compounds have been found in the vast majority of instances to provide some measure of improvement their use is invariably accompanied by other significant drawbacks which tend to detract considerably form their desirability. For example, many of the foregoing compounds must of necessity be employed in inordinately large proportions resulting in a depression of the melting point of the emulsion layer which, in turn, leads to such undesirable defects as reticulation, the latter becoming particularly manifest in those instances wherein the emulsion is subjected to high temperature, rapid processing. Moreover, such compound can present serious problems of fog and especially when the emulsion containing same is stored for any significant period of time under severe conditions of temperature and/or humidity. A further deterrent to the use of the compounds thus far known resides in their pronounced tendency to cause turbidity either in the wet or dry state of the emulsion layer.

In an effort to overcome or otherwise alleviate the foregoing and related disadvantages, considerable industrial research and development has centered around the provision of compounds which, when incorporated into light-sensitive silver halide emulsion layer, impart thereto acceptable photographic speed, contrast and covering power while reducing substantially any tendency of the silver halide emulsion to fog. However, despite the extensive industrial effort in this regard, the compounds thus far suggested have been found, characteristically, to provide a satisfactory measure of improvement only at the expense of other essential emulsion properties.

Concomitant with the provision of silver halide emulsions possessed of high photographic speed has been a corresponding intensification of other problems which detract considerably from the photographic quality obtainable in the final image. Particularly problematical has been the attainment of a photographic film element having the desired anti-static properties. As is generally known, in the manufacture of photographic film, a film base is coated on one or both sides with for example, a subbing composition usually comprising a dispersion of gelatin in a suitable solvent or solvent mixture so as to facilitate the adherence for anchorage of one or more of the photosensitive, non-curling or anti-halation layers. When such a laminate is wound into a tight curl and subsequently unwound, as during the coating operation, considerable static electricity is generated and spark discharges are likely to occur. The foregoing phenomena is invariably manifested following development of the exposed film in the form of black streaks, lines, or other irregularities which tend to create a fog pattern throughout the entire emulsion layer. In general, such spurious density deposite become more pronounced as the sensitivity and thus speed of the film material is increased. Consequently, the provision of improved sensitizing agents has made it incumbent upon the film processor to include in the film element a substance which abates or otherwise retards the tendency of such film to accumulate such static charge or alternatively a substance which is an electrolyte or possesses hygroscopic properties in order to impart conductivity to the film and thereby expedite dissipation of such static charges before their accumulation leads to local electrical discharge.

As will be recognized, impairment of image quality becomes more pronounced, in general, as the photographic speed of the emulsion material is increased.

In co-pending application Ser. No. 319,969, filed Oct. 30, 1963, there is described a novel class of silver halide emulsion sensitizer materials comprising certain watersoluble oxide adducts of gelatin. Such materials have been ascertained to function to exceptional advantage as photographic sensitizing agents while reducing to a great extent the objectionable features which invariably attend the use of the more conventional sensitizers. Despite the number of advantages presented by such water soluble gelatin derivatives, it has nevertheless been observed that photographic elements containing same are not possessed of optimum anti-static properties, i.e., to the extent that any requirement for the additional and conjoint use of specific antistatic compounds is necessarily obviated.

In accordance with the discovery forming the basis of the present invention it has been determined that the employment of water-soluble oxide adducts of gelatin, further derivatized, makes possible the obtention of the advantageous speed-imparting characteristics of such compounds while at the same time providing the film element containing same with vastly improved anti-static properties.

Thus, a primary object of the present invention resides in the provision of improved light-sensitive silver halide emulsions as well as photographic elements fabricated therewith in which the aforediscussed disadvantages are eliminated or at least mitigated to a substantial extent.

A further object of the present invention resides in the provision of improved light sensitive silver halide emulsions characterized by outstanding improvement in photographic speed, contrast and covering power.

Anotherobject of the present invention resides in the provision of improved light-sensitive silver halide emul sions having exceptional anti-static properties and characterized by exceptional stability, e.g., resistance to fogging, despite subjection to conditions of high temperature and/or humidity.

Other objects and advantages of the present invention will become apparent hereinafter as the description thereof proceeds.

The attainment of the foregoing and related objects is made possible in accordance with the present invention which, in its broader aspects provides bringing into operative association, i.e., contact, with a light sensitive photographic emulsion, a water-soluble phosphoric acid ester of a polyoxyalkylenated derivative of gelatin.

The novel sensitizers of the present invention may be readily prepared by treatment in solvent media of a polyoxyalkylenated gelatin derivative of the type described in co-pending application Ser. No. 319,969, with a suitable phosphating agent, e.g., phosphorous pentoxide (P The polyoxyalkylenated gelatin derivatives may be prepared according to the procedure described in copending application Ser. No. 319,969. Such procedures comprise in general heating one part of gelatin with from about 0.8 to about 5 parts of an alkylene oxide i.e., a Vic-epoxy compound preferably containing from 24 aliphatic carbon atoms e.g. ethylene oxide, propylene oxide, 1,2-butylene oxide, styrene oxide, etc. at a temperature ranging from about 80 to about 200 C. in the presence of suitable catalyst material, e.g., alkoxides, oxides and hydroxides of lithium, potassium, sodium, calcium, zinc and lead with preferred catalyst materials comprising the alkali metal hydroxides, particularly sodium hydroxide and potassium hydroxide. The nature of the gelatin material employed for oxyalkylenation is not particularly critical and may be selected from any of those promulgated in the art for photographic applications. Particularly beneficial results are obtained in accordance with the present invention with the use of polyoxyalkylenated gelatin derivatives having a molecular Weight within the range of from about 80,000 to about 160,000. It should be recognized however that the aforestated molecular weight range connotes materials found to assure optimization of the improvements described herein; thus, specific applications may dictate the propriety of utilizing polyoxyalkylenated gelatin materials having a molecular weight falling without such range.

While the exact structure of the gelatin is not known, it occurs in bones, hides, skins and sinews and can be readily obtained from the parent substance colagen, by

well known prior art techniques which usually involve some form of preliminary treatment e.g., degreasing in the case of bone stock, and liming or acidulation in the case of hide and sinew stocks by which the material is converted to a form suitable for the cooking operation. The raw material so treated is converted to gelatin by hydrolysis, i.e., by heating in water to yield a solution which may be concentrated by vacuum evaporation and subsequently spray or drum dried to yield a gelatin product which may be recovered in a variety of forms, sheets, flakes, powder, pearls or noodles depending upon the mode of processing.

The polyoxyalkylenated gelatin obtained as described previously is thereafter converted to the phosphate ester by phosphation with P 0 hypophosphorous acid, etc., in inert solvent solution in the presence of suitable catalyst at slightly elevated temperatures. The amount of phosphating agent employed preferably ranges from about 95-105 moles of P 0 hypophosphorous acid etc. per mole of polyoxyalkylenated gelatin. It is preferred that the amount of phosphating agent employed be sufiicient to yield polyoxyalkylenated gelatin phosphated derivatives having an acid number within the range of from about to about 110. Suitable solvents for the phosphation reaction includes for example alkanes, alkyl chlorides, cycloalkanes, cycloalkyl chlorides, aromatic and alkylaromatic hydrocarbons or halides, alkyl or aromatic ethers, chlorides of ethoxylated alcohols or phenols or other solvents inert to the P 0 used in the reaction. Suitable catalysts may be included, optionally, in order to accelerate or otherwise expedite phosphate ester formation although the desired phosphation reaction readily proceeds in the absence of such materials.

As mentioned hereinbefore, the novel sensitizing agents of the present invention augment to a considerable extent the anti-static properties of film materials containing same. Although typical in many respects, such copounds present the significant and unique advantage in that any requirement for the use of special antifogging agents in conjunction therewith is eliminated. The commercial importance of this aspect cannot be stressed too vigorously since heretofore photographic sensitizers of the polyoxyalkylenated variety, e.g., those of the type obtained by the condensation of alkylene oxide with glycols, aliphatic amines, ethers, esters, amides, etc., have produced intolerable degrees of fogging with the use of the more conventional antifoggant materials. Consequently, it was necessary to resort to the use of special and costly antifoggants in order to reduce the fogging problem to a level consonant with commercial requirements.

In contradistinction, the polyoxyalkylenated gelatin phosphate esters of the present invention may be readily employed in combination with conventional, antifoggant compounds in the virtual absence of such deleterious fogging effects. Moreover, it was particularly surprising to discover that such sensitizers may be employed to exceptional advantage in combination with the more conventional polyalkylenated derivatives, such as those mentioned in the aforecited prior art, such combinations providing synergistic sensitizing effects, i.e., imparting high sensitivity to photographic silver halide emulsions incorperating same with a minimum of fog while simultaneously eliminating substantially problems associated with static charge build-up on the photographic element.

The improvements made possible by the present invention may be realized by incorporating the polyoxyalkylenated gelatin phosphate ester in the light sensitive silver halide emulsion layer, and undercoating, intermediate coating, overcoating and/or surface coating. The proportions employed will depend to a great extent on the particular situs of such compounds as well as the type of emulsion employed. For example, with silver halide emulsions of the high speed ammonia type, it is found that the use of such phosphate esters in concentrations ranging from 1 to about 4 grams per mole of silver halide is particularly beneficial. When incorporated into a non-sensitized auxiliary layer, undercoating, etc., it is in general preferred that somewhat higher concentrations be employed, e.g., within the range of from about 2 to about 20 grams per mole of silver halide. With embodiments of the latter type, higher concentrations are advisable in order to assure that a suflicient amount of phosphate ester will be brought into operative association with the sensitized emulsion layer e.g., during development, to thereby realize the improvements contemplated herein. Without intending to be bound by any theory, it has been postulated in explanation of the synergistic improvements made possible by the present invention, that the phosphate ester characteristically diffuses or otherwise migrates to the sensitized emulsion layer and especially in the presence of solvent media, thus bringing about the desired intimacy of contact with the silver halide grains. In most applications, it is found that concentrations of phosphate ester within the range of from about 1 to about grams regardless of where situated in the photographic film element will be eminently satisfactory.

When added to the emulsion layer, it is preferred that the addition of polyoxyalkylenated gelatin phosphate ester be effected during the actual preparation of the emulsion either before or after the emulsion washing step. If sensitizing dyes are to be included in the sensitized emulsion, the phosphate ester may be added either before or after dye addition.

The following examples are given for purposes of illustrating the present invention only and are not to be regarded in any way as being limitative thereof.

EXAMPLE I Preparation of polyoxypropylenated gelatin A 30% gelatin solution in water is prepared. The solution temperature is maintained at 40 C. -while propylene oxide is bubbled therethrough for a period of approximately 20 minutes. The polyoxypropylenated gelatin product obtained is characterized by lower gelatin strength while the melting point dropped from 39 C. to 365 C.

Approximately 100 parts of the polyoxypropylenated gelatin product obtained above is charged to a solution comprising 200 parts of GAP Igepal chloride and 1 part of hypophosphorous acid, with agitation, the solution temperature being maintained at a temperature ranging from 30 to 35 C. throughout the addition. The aforementioned Igepal chloride comprises a polyether material commercially available from the General Aniline & Film Corporation and corresponds to the condensation product of nonylphenol with moles of ethylene oxide. A terminal chlorine atom is introduced into the polyether chain by means of thionyl chloride treatment. Approximately 14.2 parts of phosphorous pentoxide (P 0 is charged to the solution over a period of approximately 2 hours the solution temperature being maintained within a range of from 30 to 55 C. throughout. Upon completion of the phosphorous pentoxide addition, the solution medium following a nitrogen purge, is heated to a temperature ranging from 80 to about 85 C. and held at this temperature for a period of approximately 2 hours in order to assure complete dissolution of all phosphorous pentoxide. The solution is thereafter bleached at 70 C., and heated to a temperature ranging from 80 to 85 C. for approximately 5 minutes and thereafter allowed to cool to room temperature. The product obtained was identified as being the phosphate ester of polyoxypro pylenated gelatin having an acid number of 98.

Examples 11 through V illustrate specifically the use of the aforedescribed phosphate esters in connection with the preparation and processing of photographic film. elements.

EXAMPLE II A silver halide emulsion in gelatin containing 2% silver iodide and 98% silver bromide is prepared in a conventional manner and brought up to its maximum lightsensitivity. It is then readied for coating on film base, that is, melted at 40 C., necessary coating finals are added such as sensitizing dyes, stabilizers and hardeners. A 10% aqueous solution of the polyoxypropylenated gelatin phosphoric acid ester described in Example I is prepared and 10 cc. of this solution is added to a sample of the above described emulsion, Containing about 0.4 mole of silver halide. A sample of the same emulsion, but not containing the speed increasing additive, serves as a control. The so prepared emulsion samples are coated on a suitable cellulose ester base and dried. Samples of these film coatings are then exposed in a Type IB Sensitometer, developed in a developer of the following composition:

Distiller water ml 500 Metol grams 2.2 Sodium sulfite, anhydrous d0 72 Hydroquinone do 8.8 Sodium carbonate, monohydrate do 56 Potassium bromide do 4 Water to make 1.0 liter.

Fog, 6

Relative Fog days oven Phosphoric acid ester of speed, after test and polyoxypropylenated gelatin, gram 6 dev. 12 dev. 6 dev.

EXAMPLE III Relative speed, 6 dev.

Fog after 12' dev. .38

Fog, 6 days oven test and 6' dev. .26

EXAMPLE IV A silver halide emulsion in gelatin containing 2% silver iodide and 98% silver bromide was coated on film base in a manner known to the art. After the coating was applied, an aqueous gelatin solution containing 20 grams of gelatin per liter and 1.2 grams of phosphoric acid ester of polyoxypropylenated gelatin was coated thereon as an antiabrasion layer. After drying, film samples were exposed and processed as described in Example II. The samples described exhibited a relative speed of 130 with a fog of .13 as compared with a type coating of the same emulsion having an antiabrasion layer similar to that described above, but lacking the speed increasing additive and having a speed of 100 and a fog of .13.

EXAMPLE V A silver halide emulsion in gelatin containing 2% silver iodide and 98% silver bromide is coated on a film base in a manner well known in the art. An aqueous gelatin solution containing 20 grams of gelatin per liter is prepared and divided into three samples identified as (a), (b) and (c) respectively. To sample (a) is added 1.2 grams of polyoxyethylene lauryl ether. To sample (b) is added 2.4 grams of polyoxyethylene lauryl ether and to sample (0) is added a mixture comprising 1.2 grams of polyoxyethylene lauryl ether and 1.2 grams of phosphoric acid ester of polyoxypropylenated gelatin. Each of the so prepared compositions is thereafter applied to three separate elements, as described previously, as antiabrasion layers, i.e., directly overcoating the light-sensitive silver halide gelatin layer. Each of the film samples is then exposed and processed in a manner identical with that described in tabulated below:

Example II. The results obtained are The improved anti-static properties characterizing the polyoxyalkylenated gelatin phosphoric acid esters of the present invention can be made readily manifest by reference to the following discussion. A coating solution (sample (a)) comprising an aqueous gelatin solution containing 20 grams of gelatin per liter and 1.2 grams of phosphoric acid ester of polyoxypropylenated gelatin is evaluated in terms of static susceptibility expressed in surface resistivity (10 megohms). The results obtained are compared with a similar gelatin composition but omitting the phosphate ester material (sample (b) The static susceptibility evaluations are carried out at 72 F. at varying humidities. The results obtained are summarized from the following table:

Surface resistivity (10 megohms) 13% 22% 40% relative relative relative humidity humidity humidity S ample Results similar to those described above are obtained when the procedures exemplified are repeated but employing in lieu of the polyoxypropylenated gelatin phosphoric acid ester, the phosphated derivatives of gelatin adducts obtained by condensation with:

ethylene oxide 1,2-butylene oxide styrene oxide sible by the present invention will be very much in evidence.

Although the subject invention has been explained with particular reference to the use of gelatin in the silver halide-dispersion forming step, it will be understood that other maten'als may be employed in part for such purposes. Thus, the gelatin may be utilized in suitable admixture with any of the water-sensitive, i.e., water soluble and/or water permeable organic colloids including polymeric materials of both synthetic and natural origin.

The present invention has been disclosed with respect to certain preferred embodiments thereof, and there will become obvious to persons skilled in the art various modifications, equivalents or variations thereof which are intended to be included within the spirit and scope of this invention.

What is claimed is:

1. A light-sensitive silver halide emulsion containing as a sensitizer agent a compound comprising a water soluble phosphoric acid ester of polyoxyalkylenated gelatin.

2. A light-sensitive silver halide emulsion according to claim 1 wherein said sensitizer agent comprises the phosphoric acid ester of polyoxypropylenated gelatin.

3. A light-sensitive photographic material comprising a base and at least one light sensitive silver halide emulsion, said light sensitive material containing as a sensitizer agent a compound comprising a water soluble phosphoric acid ester of polyoxyalkylenated gelatin.

4. A light-sensitive photographic material according to claim 3 wherein said sensitizer comprises a water soluble phosphoric acid ester of polyoxypropylenated gelatin.

5. A light-sensitive photographic material according to claim 3 wherein said sensitizer agent is present in a light sensitive silver halide emulsion layer.

6. A light-sensitive photographic material according to claim 3 wherein said sensitizer agent is present in a layer in contact with said light-sensitive halide emulsion layer.

References Cited UNITED STATES PATENTS 3,312,553 4/1967 Dersch 96107 FOREIGN PATENTS 1,015,023 12/1965 Great Britain 96-107 OTHER REFERENCES The Theory of the Photographic Process, 3rd ed., Mees-James, 1966, p. 45, published by MacMillan Co., New York.

NORMAN G. TORCHIN, Primary Examiner R. E. FICHTER, Assistant Examiner 

